1. Field of the Invention
The invention relates to a molding composition based on a polyamine-polyamide copolymer and an article produced from the same by blow molding.
2. Discussion of the Background
The blow molding process is usually used to produce hollow articles, such as bottles, tanks, tubing, etc. In traditional extrusion blow molding, the parison is extruded vertically downward. Once it has reached a sufficient length, is shaped in a mold by injecting air, to obtain the finished part. More recent developments in the engineering of the machinery have led to other versions of blow molding, e.g. to 3D blow molding, in which an appropriate handling unit places the parison into a three-dimensional cavity. Another version of the process which should be mentioned is suction blow molding, in which the parison is sucked into a closed cavity. The following references describe conventional blow molding processes: F. Hensen, W. Knappe, H. Potente (ed.), Handbuch der Kunststoff-Extrusionstechnik II/Extrusionsanlagen [Handbook of plastics extrusion technology II/extrusion systems], Carl Hanser Verlag Munich, Vienna 1986, Chapter 12, and F. Schxc3xcller, Plastverarbeiter, Volume 49, No. 7, pp. 56-59. Coextrusion blow molding is described in W. Daubenbxc3xcchel, Kunststoffe 82 (1992), pp. 201-206.
A common feature of these blow molding processes is that high melt stiffness is required to minimize parison drawdown caused by gravity. However, in the case of polyamide it is impossible to provide the underlying molding composition with sufficiently high melt stiffness, in particular for large moldings, at reasonable melt viscosities. Another problem here is that, compared to polyethylene, for example, polyamides are more difficult to cut. This causes major problems when cutting or break-off methods are used to remove xe2x80x9cflashxe2x80x9d.
To overcome the above problems, various polymer systems have been suggested. For example, branched copolymers based on polyamine and polyamide are known, and may be prepared, for example, by cationic polymerization of caprolactam in the presence of polyethyleneimine hydrochloride dendrimers as core molecule (J. M. Warakomski, Chem. Mater. 1992, 4, 1000-1004). Compared with linear nylon-6, nylon-6 dendrimers of this type have markedly reduced melt viscosity and solution viscosity, but unchanged tensile strength, stiffness, melting points, enthalpies of fusion, and oxygen-barrier action.
Graft copolymers based on polyvinylamine and polyamide are known from U.S. Pat. No. 2,615,863. U.S. Pat. No. 3,442,975 describes graft copolymers prepared by polymerizing lactams in the presence of high-molecular-weight polyethyleneimine.
DE-A 19 15 772 describes blends made from a polyimine-polyamide graft copolymer and from a polyolefin, and/or polyester, these can be processed to give fibers which are easy to dye.
DE-A 196 54 179 describes H-shaped polyamides which are prepared from lactams and, respectively, aminocarboxylic acids, and from an at least trifunctional amine, and from bifunctional carboxylic acids and monofunctional carboxylic acid, there being a particular ratio between the two latter and between these and the functional groups of the at least trifunctional amine. The products have improved melt stability.
WO-A 96/35739 moreover describes specific star-shaped branched polyamides whose melt viscosity has only low dependence on shear rate.
Finally, the German patent applications 100 05 640.7 and 100 05 639.3, which are not prior publications, describe polyamine-polyamide graft copolymers. It is apparent from the above references that copolymers of this type generally have good flowability.
It is an object of the present invention to provide a polyamide molding composition which has high melt stiffness and is suitable for blow molding applications and which when compared with polyamide molding compositions conventionally used, is easier to cut.
This and other objects have been achieved by the present invention the first embodiment of which includes a molding composition, comprising:
at least 50% by weight of a polyamine-polyamide copolymer;
wherein said molding composition is obtained from the following monomers:
a) from 0.05 to 2.5% by weight of a polyamine having at least 4 nitrogen atoms based on the polyamine-polyamide copolymer, and
b) a polyamide-forming monomer selected from the group consisting of a lactam, a xcfx89-aminocarboxylic acid, an equimolar combination of a diamine and a dicarboxylic acid and a mixture thereof,
wherein the polyamine-polyamide copolymer has the following properties:
a viscosity of at least 5 000 Paxe2x80xa2s at 250xc2x0 C. and at a shear rate of 0.1 l/s; and
a viscosity ratio of at least 7 at 250xc2x0 C., when the melt viscosities at shear rates of 0.1 l/s and 100 l/s are compared with one another.
The invention further provides for a method of blow molding the above composition and for a blow-molded article.